Acrylic composite fibers having irreversible three - dimensional coil crimps



Exhausted Dye owf) HIDETO SEKIGUCHI ETAL 3, 1 ACRYLIC COMPOSITE.FIBERSHAVING IRREVERSABLE THREE DIMENSIONAL COIL CRIMPS Filed March 24, 1967I, I I I I I I5 p05 I20 Dyeing Time (min.

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United States Patent US. Cl. 161-173 6 Claims ABSTRACT OF THE DISCLOSUREAn acrylic composite fiber comprising two different acrylic polymercomponents laminarly conjugated together along the length of the fiber,said components consisting predominantly of acrylonitrile butcopolymerized with at least one hydrophobic non-crystalline highpolymer-forming comonomer in different proportions so as to causedifference in thermal shrinkage between said components, the highshrinkage component containing a strong acidic group providing dyeingsite for a cationic dye in an amount less than that in the other fibercomponent so that the initial dyeing rates of these two components aresubstantially equal and the fiber has threedimensional coily crimpswhich are irreversible even when exposed to water or other swellingagent. Each component contains 5-15% by weight of the hydrophobicnon-crystalline high polymer-forming comonomer, but there is adifference of O.5-6% by weight in content of said comonomer between thetwo acrylic polymer components.

This invention relates to acrylic composite fibers which have improvedcrimp characteristics and can be well dyed with cationic dyes. Moreparticularly the present invention relates to acrylic composite fibershaving various characteristics wherein two types of acrylic polymercomponents are uniformly laminarly arranged along the entire lengths ofthe fibers, three-dimensional coily crimps being formed due to thedifference in thermal shrinkage between the two components. Oncedeveloped these coily crimps have no water-reversibility, and thereforedefects such as are often observed in conventional acrylic compositefibers, e.g. a part of the crimps vanishing when the fibers are washed,causing elongation and therefore a decrease in the dimensionalstability, are eliminated. In the present invention, dimensions arestable even if the fibers are washed, and the two acrylic polymercomponents of different shrinkage characteristics in the same singlefiber are not delaminated or separated from each other, nor is threadsplitting caused. Further, the initial rates of dyeing of bothcomponents forming the acrylic composite fibers of the presentinvention, with a cationic dye, are substantially equal, and bothcomponents have an even or level dyeability. The fibers of thisinvention have an excellent woolly elasticity and hand.

Many efforts have been made to impart excellent woolly elasticity andhand to synthetic fibers. This has been attained to a considerabledegree in certain acrylic composite fibers. However, the conventionalacrylic composite fibers exhibit only an imitation of a part of theproperties of wool and are neither woolly in their entirety nor havecharacteristics superior to the properties of wool. As regards thedimensional stability, for example, in washing, woolen products have adefect in that, as washing is repeated, due to the peculiarshrinkability in addi tion to the water-reversibility of the crimps,they will shrink remarkably. Further, the invention of Breen disiceclosed in US. Pats. Nos. 3,038,236, 3,038,237 and 3,039,- 524, which isconsidered to be one providing typical con- 'ventional acrylic compositefibers, gives a product having water-reversible crimps by conjugatingtwo components having a difference in the ionizing radical contents. Inaddition the principle of Sisson, noted in US. Pat. No. 2,439,815, givesan excellent elasticity and hand. However, acrylic composite fibersbased on this principle have great disadvantages. The dimensionalinstability in washing is one of such defects. That is to say, there isa defect in that, since a part of crimps will vanish and decrease whenwet, the fibers will elongate when the fibers are washed. Thus, whilewool has a defect in that it will shrink remarkably, the acryliccomposite fibers by the invention of Breen have a defect in that theywill elongate.

According to Breen, the water-reversible crimps are of such propertythat, with the action of water or other swelling agent, the amount ofcrimps will vary and, when the swelling agent is removed, the originalcrimped state will be restored. In the testing method shown in theexample of Breens US. patents, this is called an equilibrium crimpreversibility, which is a value obtained after the fibers are left in awet state at 70 C. for 6- hours and are then dried at 70 C. for 16 to 24hours and this treatment is repeated until the dry-wet crimp differencebecomes constant. However, in the step of processing fiber products orin the process of wearing them as clothes or repeating the washing anddrying of them, the conditions of such high temperature and long time as70 C. in a wet state for 6 hours and 70 C. in a drying process for 16hours cannot feasibly be adopted. In case the crimps vary in the dry andwet states, such deformations as extension, shrinkage, bend and twistwill occur in every part of the fibers. However deformations of thefibers will be subject to a decisive velocity influence from thetemperature, medium and time in the environment. For example, even iffibers have fixed crimps in equilibrium at a fixed temperature in afixed medium, the equilibrium value will be obtained only when thefibers are placed in the particular environment for a sufficient lengthof time. Even if the equilibrium value is obtained under such testingconditions as are defined by Breen, in practical use there will beobtained only a value in the course of variation proceeding to theequilibrium value. That is to say, formation of the crimps will bedetermined by the velocity of the variation to the equilibrium value andthe crimps will be obtained only when sufficient time has lapsed toachieve the equilibrium value. More particularly, if the wetting anddrying temperature and time conditions are respectively different, thewater-reversible crimps will be of degrees which differ accordingly. Forexample, in summer and winter, the washing and drying temperatures aredifferent. Further, in domestic washing and commercial washing, therespective temperature and time conditions are different. Even in thedyeing process, the same thing is presumed. Even if any one of thesedifferent conditions is present, no sufficient equilibrium crimp valuewill be obtained. In all cases, only crimps of respectively differentdegrees will be obtained. products having many crimps shrink well andare high in the elasticity. On the other hand, products having fewcrimps tend to extend, are low in the elasticity, are therefore low inthe dimensional stability and fluctuate remarkably in elasticity andhand. What is more important is that generally, in the process ofworking or practicing clothing products, under wet conditions thedeformations of the fibers are more in a process of ahigher variationvelocity. It has been discovered that synthetic fibers containing alarge amount of an ionizing radical in the invention of Breen, which isdeemed specifically as a typical ex- 3 ample of acrylic compositefibers, tend strongly to become deformed by water so that the variationvelocity of crimps is higher in the wet state even under the sametemperature and time conditions. Therefore, generally,

in the water-reversible crimps, the rate at which the crimps vanish andthe dimensions elongate due to water is higher than the rate at whichthe crimps return and shrink due to drying. That is to say, in the knownprocess, as the wetting and drying are repeated, the crimps will tend todecrease and the dimensions will tend to extend.

It has been discovered that, due to coily crimps of composite fibers,the elastic recovering property will rise and therefore an excellentwoolly elasticity and hand will result, but in fibers havingwater-reversible crimps, the crimp retention and dimensional stabilityare so low that coily crimps cannot be a feasible means of overcomingthedefects of the deterioration of the elasticity and hand, due towashing and the dimensions being likely to extend.

Therefore, an object of the present invention is to provide an acryliccomposite fiber product which has the same elasticity as wool, due toirreversible coily crimps of acrylic composite fibers, does not soremarkably shrink as wool as regards the stability of the dimension andform, does not have the defect that, in the repetition of wetting anddrying, the crimps vanish and the fibers extend as in conventionalwater-reversible acrylic composite fiber products, and has a permanentlystable crimpability.

Another object of the present invention is to make the initial rates ofdyeing of both components (referred to as A and B) of acrylic compositefibers, with a cationic dye, equal to each other. This is very importantin the dyeing process. I

In Breens US. patents considered to be a typical example of conventionalacrylic composite fibers, the ditference in the content of an ionizingradical which is a dyeing site of acrylic fibers in both components isutilized as a means of giving water-reversible crimps. This results insome difiiculties, as the ionizing radical is used for both the dyeingsite and the means of obtaining waterreversible crimps. Specifically,from the viewpoint of dyeing, the difference in the content of theionizing radical between the two components of composite fibers 1Sunduly large so that the dyeabi lity will become different between thetwo components and therefore the uniform property of dyeing willdeteriorate. After dyeing, the degree of dissociation of the ionizingradical will dirrnmsh and hence the hydrophilicity will decrease,resultlng in a remarkable decrease of crimps. Further, the difference inthe properties of both components of the composite fibers will be soremarkably large that the yarn will be likely to delaminate or splitinto the two components.

It has been discovered that the above drawbacks are overcome and theobjects of the invention are accomplished by providing acrylic compositefibers which have been wet-spun and in which two or more types ofacrylic polymer components, different in their thermal shrinkage, areuniformly laminarly arranged along the entire lengths of the fibers.Each component contains. at least 5 to by weight of a hydrophobicnoncrystalline high polymer-forming comonomer in the form of a copolymerwith acrylonitrile, there being a diiference of less than 6% by weightin the content of said hydrophobic noncrystalline high polymer-formingcomonomer between the acrylic polymer components. Further, the acryliccopolymer component which is higher in the content of the hydrophobicnoncrystalline high polymerforming comonomer (that is, the componentexhibiting higher thermal shrinkage) is made to contain a strong acidradical, forming a dyeing site for a cationic dye bonded with thepolymer, in an amount which is smaller by 4 to 30 milliequivalents per10 grams of the polymer than the amount which is contained in thecopolymer component which is lower in the content of the hydrophobicnoncrystalline high polymer-forming comonomer (that is, the copolymercomponent exhibiting lower thermal shrinkage). In this way the initialdyeing rates of both components with the cationic dye will besubstantialy equal to each other. The resulting heat treated fibers havethree-dimensional coily crimps irreversible in water and other swellingagents.

According to the present invention, each component is copolymerized withat least 5% by weight and at most 15% by Weight of a hydrophobicnoncrystalline high polymer-forming comonomer, and there is a differenceof less than 6% by weight of the hydrophobic noncrystalline highpolymer-forming comonomer between the two components. The respectivepolymers are simultaneously and compositely spun, through a commonorifice in an art-recognized manner. Thus a difference of more than 1%in the thermal shrinkage between the components during drawing andheat-treating the spun yarn is created due to the difference in contentof the said comonomer. Further, the content of the strong acid radi calin the high shrinkage component is from 4 to 30 milli-equivalents per 10grams of the polymer less than the content in the low shrinkagecomponent, thus cancelling the difference in the Water-swellability (andhence water-reversibility of crimps) caused by the differences in thedegree of orientation and the cohesive energy in the noncrystallineregions of both components. The coily crimps to be developed due to thedifferences in the degree of orientation and the cohesive energy in thenoncrystalline region are indicated by the likelihood of the fibersbeing deformed in hot water at C. or, for example, the reciprocal numberof the modulus of elasticity in hot water at 90 C., that is, acompliance 1 But the fiber components higher in the compliance 1,, inhot water are much higher in their swellability in hot water that, evenif the ionizing radicals of both components are made equal, thewater-reversibility of the crimps will not be able to be removed. Eachcomponent is made to contain 5 to 15% by weight of the hydrophobicnoncrystalline high polymer-forming comonomer. In case the content isless than 5% by weight, in the aqueous wet spinning, the fiber gelswelling degree after coagulation will be so high that the shrinkage indrying will be high, and therefore substantially no shrinkingperformance will be observed in the subsequent heat-treating operation,and the degree of the noncrystalline region production will be low.Further, a content of less than 5% of said comonomer will not bedesirable from the viewpoint of dyeability. When the content is morethan 15% by weight, the softening point will be lower, and theheat-resistance will be remarkably lower.

The difference In the hydrophobic noncrystalline high polymer-formingcomonomer content between both components is kept 6% or less by weight.If there is a difference of 6% by weight at most, coily crimps necessaryand sufiicient to elevate the elasticity, as of knitted and wovenproducts, will be obtained. If there is a difference larger than that,the degree of yarn delamination in the two components will be so highthat acrylic composite fibers having permanent crimps will not beobtained. Further, if the difference in content of the non-crystallinehigh polymer-forming comonomer between both components is 0.5% byweight, the objects of the invention are attained.

The high thermal shrinkage component polymer is made to contain, asbonded with the polymer, the strong acid radical forming a dyeing sitefor a cationic dye in an amount smaller by 4 to 30 milli-equivalents per10 grams of the polymer than in the other component (that is, the lowthermal shrinkage component polymer). This is based on the fact that thewater-reversibility of the crimps produced due to the ditference in thecontent of the hydrophobic noncrystalline high polymer-forming comonomerbetween both components can be thereby cancelled. Furthermore, only whenthe amount of strong acid radical, forming the dyeing site of the highshrinkage component polymer is made less than that of the low shrinkagecomponent polymer by an amount of 4 to 30 milli-equivalents per grams ofthe polymer, will the initial dyeing rates of the two components with acationic dye become substantially equal to each other.

The respective components having equal initial rates of dyeing with acationic dye will not only be able to be very uniformly dyed even ifcomposite fibers having any component ratio or any distribution ofcomponent ratios are made, or even in the case of yarns spun as blendedwith yarns of an acrylic single component corresponding to one of thecomponents, but also will have a tendency to exhibit similarhydrophilicity and other physical properties of fibers equal in dyeingrate. Therefore, it is very rare that the yarn will split into the twocomponents. These facts are one of the most important features of thepresent invention.

In the high shrinkage component of the fiber of the present invention,the hydrophobic noncrystalline high polymer-forming comonomer iscontained in an amount higher than in the low shrinkage component butthe content of the strong acid radical which is a dyeing site for acationic dye is less than that in the low shrinkage component.Therefore, such physical properties as the swellability with water ofboth components are substantially equal and the uniform dyeing effect ofboth components in the initial period of dyeing with the cationic dye isremarkably promoted. Therefore, the yarn split is less than in theconventional acrylic composite fibers. The difference in the thermalshrinkage between both components which can be utilized to obtain thepractically necessary permanence of crimps and even dyeability, that is,the range of the copolymer composition can be adopted more widely thanin conventional composite fibers.

In the present invention, the initial dyeing rates of both components ofcomposite fibers with a cationic dye are made substantially equal.Uniform dyeing is important particularly in the case of light colordyeing. Its decisive influence is given by the initial dyeing rate atthe beginning of dyeing. Therefore, the dyeing is begun generally at alow dyeing rate by a method of gradually elevating the dyeing bathtemperature so that an even dyeing may be obtained.

Tentatively, the initial dyeing rate has been determined by thefollowing manner. The filters are dyed at a dyeing bath temperature of90 C. for 60 minutes with Sumiacryl Orange 3R (produced by SumitomoChemical Co., Ltd.) as a cationic dye, under the following dyeing bathconditions: a dye concentration of 7% of the weight of the fibers(abbreviated as OWF hereinafter), 3% OWF acetic acid and a bath ratio of1/100. The initial dyeing rate is represented by the exhausted amount ofthe dye on the fibers in percent OWF in this standard condition. Wefurther obtained isothermal dyeing curves and investigated the initialdyeing performances. It has been recognized from the dyeing curves shownin the accompanying drawing that, as the number of dyeing sites of thehigh shrinkage component is made less than the number of dyeing sites ofthe low shrinkage component to make the initial dyeing rate of bothcomponents substantially equal, and as the equilibrium is approached dueto dyeing for a long time, the dyed amount of the high shrinkagecomponent will decrease. In order to make the dyeing rates of the highshrinkage component and low shrinkage component equal to each other andto eliminate the water-reversibility of the fibers, though the dyeingrate will differ depending on the difference in the compliance 1 betweenboth components, the number of coily crimps, and the level of the totalamount of the dyeing sites and also depending on whether the level ofsuch total amount of the dyeing sites is to be equal to the number ofwoolly crimps as is required for thick color dyeing of acrylic fiberswith a cationic dye, it will be necessary to make the content of thestrongly acid radical in the high shrinkage component less than thecontent of the strongly acid radical in the low shrinkage component byat least 4 milli-equivalents per 10 grams of the polymer at the minimum.Further, as a result of investigations, it has been found that, when adifference of 30 milli-equivalents per 10 grams of the polymer is givenas the maximum, the objects of the present invention will be attained.When a difference larger than 30 milli-equivalents per 10 grams of thepolymer is given, the waterreversibility of the crimps will be in thenegative direction, that is, the crimps will increase when wet but willdecrease when dry and therefore it will not be desirable from theviewpoint of the stability of the crimps.

The hydrophobic high polymer-forming comonomers to be copolymerized withacrylonitrile in the present invention are those which are substantiallyinsoluble in water, and do not readily form crystalline high polymers.Examples of such comonomers are acrylic esters such as methyl acrylate,ethyl acrylate, butyl acrylate, octyl acrylate, methoxyethyl acrylate,phenyl acrylate, cyclohexyl acrylate, dimethylaminoethyl acrylate; thecorresponding methacrylic esters; vinyl chloride, vinylidene chloride,vinylidene cyanide, styrene, their alkyl substitutes; unsaturatedketones such as methyl vinyl ketone, phenyl vinyl ketone, isopropenylmethyl ketone; carboxylic acid vinyl esters such as vinyl formate, vinylacetate, vinyl propionate, vinyl butyrate, vinyl thiol acetate, vinylbenzoate; vinyl ethers and esters of ethylene anti-carboxylic acids suchas fumaric acid, citraconic acid, mesaconic acid, aconic acid, etc.

For introducing the strong acid radical into the copolymers forming theacrylic composite fibers in the present invention, there may be utilizeda method wherein a sulfonic acid radical produced by the decompositionof a catalyst in the polymerizing reaction is introduced into theterminal radical of the polymer. However, the most general method iswherein sulfonic acid radicals are positively introduced into thecopolymer. For example, a monomer which contains unsaturated sulfonicacid radical such as an alkenyl aromatic sulfonic acid, p-styrenesulfonic acid, vinyl sulfonic acid, allyl sulfonic acid or methallylsulfonic acid or their salts, and can be copolymerized withacrylonitrile, is copolymerized with acrylonitrile. Other unsaturatedorganic sulfonic acids such as 0- and m-styrenesulfonic acid,allyloxyethylsulfonic acid, methallyloxyethylsulfonic acid,allyloxypropanolsulfonic acid, allylthioethylsulfonic acid,allylthiopropanolsulfonic acid, isopropenylbenzenesulfonic acid,vinylbromobenzenesulfonic acid, vinylfluorobenzenesulfonic acid,vinylmethylbenzenesulfonic acid, vinylethylbenzenesulfonic acid,isopropenylbenzenesulfonic acid, vinylhydroxybenzenesulfonic acid,vinyldichlorobenzenesulfonic acid, vinyltrihydroxybenzenesulfonic acid,vinylhydroxynaphthalenesulfonic acid,sulfodichlorovinylnaphthalenesulfonic acid,vinylhydroxyphenylmethanesulfonic acid,vinyltrihydroxyphenylethanesulfonic acid, 1 isopropylethylene-l-sulfonicacid, l-acetylethylene-l-sulfonic acid, naphthylethylenesulfonic acid,propenesulfonic acid, butenesulfonic acid, hexenesulfonic acid and theirsalts may also be used.

It is not desirable that the content of the strong acid radical in thepolymer forming the acrylic composite fibers in the present inventionexceed 100' milli-equivalents per 10 grams of the polymer. That is tosay, in the acrylic composite fibers of a composition in which more than5% by weight of a hydrophobic noncrystalline high polymerformingcomonomer is copolymerized, as the content of the strong acid radicalexceeds milli-equivalents per 10 grams of the polymer, defects result,such that the water absorption even at the normal temperature willincrease, Youngs modulus will be likely to diminish due to the action ofwater or other swelling agents, the reversibility of the crimps will belikely to develop, the dyeing rate will become unduly high, and spots oruneven dyeing will occur in dyeing, or specifically light color dyeing.

It is preferable that each of the composite fiber components comprisesat least 85% by weight of acrylonitrile.

The composite fibers of this invention may be spun in any proper deviceknown in the art of the production of composite fibers. For example, aspinning apparatus of the type shown and described in US. Pat. No.3,182,106 may conveniently be used.

The invention will be described in more detail by referring to thefollowing examples wherein all percentages are by weight unlessotherwise specified and wherein various values have been determined inthe following manners:

The content of the strong acid radical in the acrylic polymer wasmeasured by passing a dimethyl forma-mide solution of the copolymerthrough an ion exchange resin to convert the strong acid radical intothe form of a free acid and then conductometric titration with a causticsoda solution was employed. The results of the analysis are representedin milli-equivalents of the acid radical per 10 grams of the copolymer.The molecular weight of the polymer was calculated by converting themeasured value of the viscosity of the dimethyl formamide solution at 30C. by using Standingers formula.

The fundamental crimp frequency (Cf) was measured by the formula:

C =number of crimps (l (l) b-a Crlmp 1ndex= X 100 (2) wherein a is thelength of the sample fiber under the initial load of 2 mg./denier and bis the length at 30 seconds later after an additional load of 50mg./denier has been placed on the fiber.

The value of the water-reversibility of the crimps, as represented byAC; in Formula 3, is deter-mined by the diiference between the value(wet at 70 C.) obtained by measuring C; defined as mentioned above afterthe crimps were relaxed in water at 70 C. for 6 hours, and the value C(dry at 20 C.) obtained by measuring Cf after the crimps were dried at70 C. for 16 hours and were cooled to room temperature:

AC=C (dry at 20 C.)C (wet at 70 C.) (3) As C; and AC; are inverselyproportional to the diameter of the fiber under a fixed shrinkagedifference and a fixed environment, it is necessary to represent fibersof different diameters as converted to a fixed standard. A fiber of 3deniers was used as a standard. It is necessary that thewater-reversibility Ac should be less than 0.85 at 3 deniers in orderthat the crimps may be substantially irreversible. The thread split ofacrylic composite fibers was represented by the percentage of the fiberwhich peeled into two components when the fiber suspended under a loadof 0.4 g./d. was rubbed with the side of a hard chrome-plated stainlesssteel bar of an octagonal cross-section rotated at 3500 r.p.m. forminutes, and the cross-section of the fiber was subsequently observedwith a microscope.

EXAMPLE 1 For the component A of acrylic composite fibers, in obtaininga copolymer of 89.0% acrylonitrile, 11.0%

methyl acrylate and a molecular Weight of 74,000, a chloricacid-sulfurous acid catalyst system was used. A slight amount of sodiummethallylsulfonate was also copolymerized 'with the acrylonitrile, andthe content of the sulfonic acid radical introduced at the terminal ofthe polymer both by means of the decomposition of the catalyst andpositive introduction, was adjusted to 38 milli-equivalents per 10 gramsof the polymer. For the component B, in obtaining a copolymer of 91%acrylonitrile, 9% methyl acrylate and a molecular weight of 74,000, theamount of sodium methallylsulfonate copolymerized with acrylonitrile,was adjusted in the same manner as in the copolymer of the component Aso that the total sulfonic acid radical content was 50 milli-equivalentsper 10 grams of the polymer. Each of both copolymers A and B wasdissolved in an aqueous solution of 48% sodium thiocyanate to prepare aspinning solution so that the copolymer concentration was 9% Filamentswetspun into an aqueous solution of 10% sodium thiocyanate at 0 C. witha composite fiber spinning apparatus shown in U.S. Pat. No. 3,182,106,in a manner such that the amounts of both components A and B were equalto each other, were drawn to 10 times their length in boiling water andwere dried in hot air at 115 C. When the. obtained acrylic compositefibers were heated in pressure steam at 123 C. for 10 minutes, due tothe difference in the thermoshrin-kage between both components, coilythreedimensional crimps of fundamental crimp frequency C; of 22developed in the fibers of 3 deniers. These crimps showed awater-reversibility value AC of 0. When each of both components A and Bwas singly spun, drawn and heated under the same conditions as above,the amount of dye exhaustion on the single component fibers was shown tobe 2.12% OWF in the component A and 2.16% OWF in the component B, thusindicating substantially equal values. The isothermal dyeing curves ofthe respective components A and B at C. coincided with each other verywell at the initial dyeing rate as shown in the drawing. Therefore, whenthe composite fibers were dyed under the same conditions to preparesamples of fiber cross-sections and the dye concentrations in bothcomponents were compared with each other under a microscope, it wasquite impossible to distinguish the two components from each other. Theyarns spun of these composite fibers and the products knitted or wovenfrom the yarns were very high in uniformity of dyeing, specifically inlight color dyeing, and showed a very fine finish. Further, no threadsplitting into the two components was observed.

EXAMPLE 2 The adjustment of the content of a strong acid radical formaking the dyeing rate uniform, and obtaining acrylic composite fibershaving no water-reversibility of crimps, can also be achieved byemploying a difference between the molecular weights of the polymers.The component A was obtained by aqueous suspension polymerization of acopolymer of 90% acrylonitrile, 10% methyl acrylate and had a molecularweight of 75,000. This copolymer contained 20 mini-equivalents of asulfonic acid radical per 10 grams of the polymer, introduced by thedecomposition of the catalyst system of Example 1. The component B wasobtained by aqueous suspension polymerization of a copolymer of 92%acrylonitrile, 8% methyl acrylate and had a molecular weight of 53,000.This copolymer contained 44 milli-equivalents of a sulfonic acid radicalper 10 grams of the polymer, by the same mechnism as in component A.

The component A copolyimer was dissolved in an aqueous solution of 47%sodium thiocyanate, the copolymer concentration being 9%, to prepare aspinning solution. The component B copolymer was dissolved in an aqueoussolution of 47% sodium thiocyanate, the copolymer concentration being12%, to prepare a spinning solution. The respective solutions of thecomponents A and B were spun into an aqueous solution of steam to obtainfibers of 3 deniers. The characteristics of the resultant fibers areshown in Table 1.

TABLE 1 Experiment No.

I II III IV V VI VII Pressure steam treating temperature C.)

Component A copolymer composition:

Molecular weight 58, 000 58, 000 82, 000 66, 000 67, 100 73, 900 84, 600Total sulfonic acid amount in rnllliequivalents per 10 grams of thecopolymer 46 43 41 39 36 32 27 Single component fibers:

Amount of dye exhaustion:

A (percent OWF) 2.30 2.28 2. 24 2.08 2.00 l. 92 2.28 B (percent OWF) 1.96 2. 16 2. I6 2. 16 2. 04 2. 04 2. 40 Composite fibers:

sodium thiocyanate at 0 C. with the same composite fiber spinningapparatus as in Example 1, so that the net weights of the respectivecopolymers were equally delivered. The thus obtained filaments weredrawn to 10 times their length in boiling water, were then dried in hotair at 115 C. and were heated with pressure steam at 125 C. for 10minutes, resulting in coily three-dimensional crimps being developed bymeans of the difference in the thermoshrinkage between both components.These acrylic composite fibers were fibers of 3 deniers. Theirfundamental crimp frequency C; was 20. Their waterreversibility valueAC, was 0.4. This water-reversibility value was negligible. Thus,products very high in dimensional stability were obtained. Thesecomposite fibers were so high in the molecular weight of the highshrinkage component and in the elatsicity and strength of the loadsupporting component in stretching the crimps that the permanence of thecrimps was very high. The amount of dye exhaustion on single componentfibers of '3 deniers obtained by singly spinning, drawing and heatingeach of the components A and B under the same conditions as arementioned in Example 1, was shown to be 1.08% OWF in the component A and1.16% OWF in the component B. Thus they had substantially equal dyeingrates.

EXAMPLE 3 The adjustment of the strong acid radical can be achieved by amethod which combines the adjustment of the molecular weight of only onefiber component, and the adjustment of the addition amount of a monomer,containing a strong acid radical, to be copolymerized with acrylonitrilein the polymer chain of the same fiber component. It is also possible tovary the kind of hydrophobic non-crystalline high polymer formingcomonomer to obtain a difference in the non-crystalline structure. Inthis example, for the component A, in copolymerizing 89% acrylonitrileand 11% vinyl acetate, a copolymer resulted in which the content of asulfonic acid radical was adjusted with the addition of nonaddition ofsodium methallylsulfonate. The variation of the molecular weight was asshown in Table 1. For component B, in the copolymerization of 91%acrylonitrile and 9% methyl acrylate, a slight amount of sodiummethallylsulfonate was copolymerized with the acrylonitrile, and, thecontent of a sulfonic acid radical was adjusted to 50 mini-equivalentsper 10 grams of the polymer. The copolymer had a molecular weight of58,000. Each of both component polymers was dissolved in an aqueoussolution of 48% sodium thiocyanate, the copolymer concentration being11%, to prepare a spinning solution. Composite fibers and singlecomponent fibers were spun under the same conditions as in Example 1,were drawn to 10 times their length, and were treated with pressureThese acrylic composite fibers showed very similar initial dyeingcharacteristics, their water-reversibility was so low as to besubstantially negligible, and they showed a feature of irreversiblecrimps.

EXAMPLE 4 The component A was comprised of 91% acrylonitrile and 9%methyl acrylate, and had a molecular weight of 58,000. The content of asulfonic acid radical at the terminal of the polymer, introduced bymeans of the decomposition of the catalyst system of Example 1, was 40milli-equivalents per 10 grams of the polymeraFor the component B, inthe copolymerization of 95% acrylonitrile and, 5% methyl acrylate,resulting in a molecular weight of 58,000, the total sulfonic acidradical content, introduced by copolymerizing a slight amount of sodiummethyallylsulfonate with the acrylonitrile, was 52 milliequivalents per10 grams of the polymer. Both components were spun, drawn and dried bythe same process as in Example 3, were heated in pressure steam at 130C. for 10 minutes. The fundamental crimp frequency C; of the coilycrimps of these acrylic composite fibers was 23 and theirwater-reversibility value AC; was 0.1.

What we claim is:

1. A wet-spun acrylic composite fiber comprising,

(a) two different acrylic polymer components laminarly conjugatedtogether along the length of the fiber,

(b) each of said components being a copolymer consisting predominantlyof acrylonitrile which has been copolymerized with 5-15% by weight of atleast one comonomer selected from hydrophobic non-crystalline highpolymer-forming monomers,

(c) said components'having a difference of 0.5-6% by weight in thecontent of said comonomer between them,

(d) said components respectively containing different amounts of strongacid groups of at most milliequivalents per 10 grams of the polymer,

(e) the smaller amount of the said acid group being present in thehigher shrinkage component which contains a larger amount of thehydrophobic noncrystalline high polymer-forming monomer,

(f) the respective components having a difference of 4 to 30milliequivalents per 10 grams of the polymer in the proportion of thestrong acid groups which impart to each of the components an equalinitial rate of dyeing,

(g) and exhibiting irreversible three dimensional coil crimps even whenthe resulting fiber is exposed to water or other swelling agent.

2. An acrylic composite fiber as in claim 1 wherein each componentcontains at least 85% by weight of acrylonitrilev 3. An acryliccomposite fiber as in claim 1 wherein the hydrophobic non-crystallinehigh polymer-forming comonomer is methyl acrylate.

4. An acrylic composite fiber as in claim 1 wherein one componentcontains methyl acrylate and the other component contains vinyl acetate.

5. An acrylic composite fiber as in claim 1 wherein the strong acidicgroup is a sulfonic acid group.

6. An acrylic composite fiber as in claim 5 wherein the sulfonic acidgroup is introduced into the polymer by copolymerizing a compoundselected from the group 12 consisting of methallyl sulfonic acid andsalts thereof with the monomers for forming said polymer.

References Cited UNITED STATES PATENTS 3,039,524 6/1962 Belck et a1.161-177 ROBERT F. BURNETT, Primary Examiner R. O. LINKER, JR., AssistantExaminer U.S. Cl. X.R.

